Conventionally, a braking apparatus has been known in which braking force is provided by generating, in a fluid pressure circuit, the fluid pressure in accordance with the operation amount of a brake pedal and by supplying the fluid pressure to the wheel cylinder in each of the wheels (see, for example, Patent Document 1). Various electromagnetic valves, such as pressure-increasing valve to be opened when fluid pressure is supplied, pressure-reducing valve to be opened when fluid pressure is released, and switch valve to be opened/closed when the supply channel of fluid pressure is switched, etc., are provided between a fluid pressure source and each of the wheel cylinders. The braking apparatus adjusts the supply/discharge amount of brake fluid to/from the wheel cylinder by controlling the opening/closing of these electromagnetic valves, and provides suitable braking force to each of the wheels by controlling the fluid pressure. Each actuator in the braking apparatus, such as these electromagnetic valves, is drive-controlled by an electronic control unit (hereinafter, referred to as an “ECU”), which is mounted in a vehicle, outputting a control command to the drive circuit of each actuator.
Such a braking apparatus executes so-called brake-by-wire braking control in which each actuator is driven by electronic control so as to obtain the demanded braking force that is calculated based on the operation amount of the brake pedal, not by directly transmitting the fluid pressure as it is to the wheel cylinder, the fluid pressure being generated by an operation of the brake pedal. Accordingly, it is needed that the ECU always functions normally, and even if the CPU, etc., breaks down, high fail-safety is demanded.
As a means for securing such fail-safety, a technique is known in which, for example, two ECU systems are provided such that, if one of the two ECU systems is breaks down, the other normal ECU system continuously executes the braking control (see, for example, Patent Document 2). In this technique, while a motor control apparatus for providing braking force to a wheel is provided for each of the wheels, a central control apparatus intensively controls a plurality of the motor control apparatuses. During a normal state, the central control apparatus calculates target braking force based on the inputs of the various sensors, and outputs a control command to each of the motor control apparatuses. Because each of the motor control apparatuses also receives the inputs of the various sensors, each of the motor control apparatuses drives the motor based on the inputs of the sensors if the central control apparatus brakes down. As a result, the minimum necessary amount of braking force can be secured.
Patent Documents
[Patent Document 1] Japanese Patent Application Publication No. 2008-174221
[Patent Document 2] Japanese Patent Application Publication No. 2001-138882